1. Field of the Invention
The present invention relates to a heating type fixing device installed in an electrophotographic image forming apparatus and an image forming apparatus such as a copier, a printer, or a facsimile machine including this fixing device.
2. Description of the Related Art
In an image forming apparatus such as a copier, a printer, or a facsimile machine, an image is formed by an image forming process such as electrophotographic recording, electrostatic recording, or magnetic recording. Then, an unfixed toner image is formed on a recording medium, such as a recording medium sheet, printing paper, sensitized paper, or electrostatic recording paper, by an image transfer method or a direct method. As fixing devices for fixing an unfixed toner image, contact heating type fixing devices, such as a heat roller type, a film heating type, and an electromagnetic induction heating type, are widely adopted.
As examples of such fixing devices, a belt type fixing device (for example, see Japanese Laid-open Patent Publication No. 2004-286922) and a SURF fixing (film fixing) type of fixing device using a ceramic heater (for example, see Japanese Patent No. 2861280) are known.
As for the belt type fixing device, recently, it is hoped to further shorten the time required to reach a printable predetermined temperature (a reload temperature) from an ordinary temperature state, such as a state when the device is powered on. Furthermore, it is also hoped to shorten the time (the first print time) to perform a printing operation after preparation for printing and completing paper ejection since receipt of a request for the printing operation (Issue 1).
Furthermore, with speed improvement of image forming apparatus, the number of sheets passed through the apparatus per unit time is increased, and the quantity of heat required is increased. A lack of the heat quantity, which is called a temperature drop, especially at the beginning of continuous printing is a problem (Issue 2).
To resolve these Issues 1 and 2, there is known a fixing device configured to directly apply heat to a whole low-heat-capacity fixing belt thereby improving the heat-transfer efficiency significantly. This fixing device further shortens the warm-up time and the first print time and solves the lack of heat quantity at the time of continuous printing, thereby being able to achieve good fixing performance even if installed in a high-productive image forming apparatus.
Incidentally, a fixing device is based on the premise that various types of recording media pass through the device; for example, a recording medium having a width smaller than the heat-generating width of a fixing member (a fixing belt) in a longitudinal direction may pass through the device. In this case, a non-sheet passing area of the fixing member does not lose heat by the recording medium, and therefore has an excess quantity of heat and has an increase in temperature. Consequently, there is a problem that deterioration of the fixing member advances, resulting in life shortening (Issue 3).
There is a need to provide a fixing device capable of fastening a sliding sheet to a heat-uniformizing member with a simple configuration without impairing the fixing performance, durability, and conveying performance.